A known image reader for reading a document is mounted on a facsimile, a copier, a scanner, or a combination thereof. The known image reader includes an auto document feeder (“ADF”) reading mechanism which automatically conveys a document, or an flat bed (“FB”) reading mechanism which reads an image. The ADF reading mechanism automatically conveys the document on a contact glass, radiates light to the document from a side opposite to the contact glass, and reads a reflection light by the image sensor to obtain the image of the document as image signals.
The ADF reading mechanism includes a guide plate which is biased toward the contact glass by a spring, and the document is conveyed between the guide plate and the contact glass. When a resilient document such as a glossy paper, is conveyed, the guide plate is raised, which may cause the document to float. Particularly, when a close-contact-type image sensor is used as the image sensor, a focal length of the image sensor is relatively short and consequently, when the document floats, it is difficult to obtain accurate focusing, e.g., it is difficult to obtain a clear image and focused.